Mn/DOT Flexible Pavement Design Mechanistic-Empirical Method Pavement Design Systems and Pavement Performance Models March 22-23, 2007 - Reykjavik, Iceland Bruce Chadbourn Assistant Pavement Design Engineer Minnesota Department of Transportation www.mrr.dot.state.mn.us
Acknowledgements Icelandic Road Administration Haraldur Sigursteinsson Nordic Road Association NordFoU Project
Pavement Design at Mn/DOT Current procedure Subgrade soil R-value, traffic, rule-of-thumb materials properties Relates to ride MnPAVE procedure Modulus of all layers, base strength, repeated load damage in HMA and subgrade Relates to structural distresses cracking, rutting
Background WESLEA Layered Elastic Analysis (5 Layers) Developed at U.S. Army Engineer Waterways Experiment Station (Van Cauwelaert et al, 1986)
ROADENT University of Minnesota (1996-1999) Dr. David Timm Auburn University Dr. David Newcomb NAPA Dr. Bjorn Birgisson University of Florida
MnPAVE Pavement Design Climate model More material types and default properties Lab and field test results Updated performance models
Climate
Modulus (ksi) 10,000 1,000 100 10 Seasons MnROAD Cell 21 Asphalt Base Soil 1 0 50 100 150 200 250 300 350 Day of Year
Criteria for Determining the Beginning of MnPAVE Seasons Season Criteria Fall 3-day Average Temperature < 17 C Winter Spring Thaw Spring Recovery Freezing Index > 90 C-days Thawing Index > 15 C-days 2 Weeks After Start of Spring Thaw Summer 3-day Average Temperature > 17 C
Temperature Model Whiplash Equation
T n i = 1 = n i = 1 T D 1 D i 2 i 2 i
5 Seasons vs. 52 Weeks Number of times the asphalt modulus (stiffness) is calculated. Affects the calculation time. Wide range of pavements were simulated. Design thickness differed by no more than 0.1 in. Default MnPAVE procedure has 5 seasons.
Structure
Material Properties New Asphalt Existing Asphalt (overlay design) Aggregate Base/Subbase Soils
loge = a 0 + + a 6 Witczak Equation a p 1 + 200 a 7 p + 4 a + 2 a ( p ) 8 1+ e p 200 3 / 8 2 ( p ) 3 / 8 ( a + a logf + a 2logη ) 11 12 + + a a 9 3 p 13 4 + a V 2 4 + a a + 10 p a 5 3 / 4 V V beff beff + V Where: E = 10-5 x Dynamic Modulus (psi) f = Load frequency (Hz) η = 10-8 x Dynamic Viscosity (cp) V beff = Effective binder content (% by vol.) P b = binder content (% by wt. of mix) p 3/4 = Cumulative % retained on 3/4 sieve V a = Air voids (% by volume) p 3/8 = Cumulative % retained on 3/8 sieve P ba = Absorption (% by wt. of aggregate) p 4 = Cumulative % retained on No. 4 sieve G b = specific gravity of binder p 200 = Percent passing No. 200 sieve G sb = Bulk specific gravity of aggregate a
Thompson (ILLI-PAVE) Equation log 10 Where: AREA E + AC = 1.48 1.76 log10 0. 26 D0 2D AREA = 6 1+ D0 + 1 2 D D E AC = Modulus of the HMA layer (ksi) T AC = Temperature of the HMA layer ( F) D 0 = Deflection at center of load (mils) D 1 = Deflection at 12 in. (305 mm) from center of load D 2 = Deflection at 24 in. (610 mm) from center of load D 3 = Deflection at 36 in. (914 mm) from center of load 0 2 + D D 3 0 AREA TAC
10,000 Cell 20 Modulus Comparison 1994-2003 Witczak and Thompson Equations 7.8 120/150 Pen. (PG 58-28) HMA Modulus (ksi) 1,000 100 10 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Witczak 20 30 40 50 60 70 80 90 100 110 120 HMA Temperature ( F)
Modulus Reduction Factor Modulus Ratio (R ) R= E*(near crack)/e* (between cracks)
250 MnROAD Class 5 Moduli 1994-1996 40 200 35 Backcalculated E (MPa) 150 100 50 30 25 20 15 10 Backcalculated E (ksi) Cells 21, 28 5 0 0 30 60 90 120 150 180 210 240 270 300 Days from Spring Thaw 0
Saturation 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Unsaturated Properties CL3 est. CL 4 est. CL 5 est. CL 6 est. CL 3 measured CL 4 measured CL 5 measured CL 6 measured 0.001 0.01 0.1 1 10 100 1000 10000 Suction (kpa)
Statewide HMA Deflections 1994-2005
Subgrade Modulus Superimposed on Soil Map
Subgrade Modulus Predictions E subgrade, MPa 250 200 150 100 Hogg (FWD) Predicted 85th % 15th % MEPDG High MEPDG Low MnPAVE 5.2 E predicted = e COV = 34% μ+ σ 2 2 μ = -7.74(CLAY 2 SILT 2 ) + 0.694(e -CLAY e -SILT ) + 3.86 σ best fit = 0.34 (range: 0.11 to 0.47) 35 30 25 20 15 E subgrade, ksi 10 50 5 0 Silty Clay Silty Clay Loam Clay Clay Loam Silt Silt Loam Loam Sandy Clay Loam Sandy Clay Sandy Loam Loamy Sand Sand 0
Traffic
Simplified Load Spectrum Input Analysis of WIM data Mn/DOT and FHWA vehicle types Axle distributions by truck type Assumptions about truck distributions Route types
MnROAD 2001 WIM Data Repetitions Steer Tandem Single Tridem 0 10,000 20,000 30,000 40,000 Axle Weight (lbs)
Vehicle Type 8 Repetitions Steer Single Tandem Tridem 0 10,000 20,000 30,000 40,000 Axle Weight (lbs)
Burnsville I-35E (Feb. 1 - Mar. 1 1992) 10,924 AADT Single Tandem Repetitions WIM MnPAVE Tridem Steer 0 10,000 20,000 30,000 40,000 50,000 Axle Weight (lbs)
Output
Questions www.mrr.dot.state.mn.us